Vacuum management system

1. A flywheel system comprising: a flywheel; a chamber within which said flywheel is provided; a passage for connecting the chamber to an inlet of a vacuum pump; and a valve which selectively opens or closes said passage, wherein the flywheel is mechanically coupled to the vacuum pump thereby to impart rotational drive from the flywheel to the vacuum pump.

2. A flywheel system according to claim 1 , wherein the valve opens or closes said passage based at least partially upon a chamber pressure value corresponding to a pressure in the chamber.

3. A flywheel system according to claim 2 , wherein the valve opens the passage when said chamber pressure value exceeds a first pressure value.

4. A flywheel system according to claim 3 wherein the first pressure value is between 4 and 8 mbar.

5. A flywheel system according to claim 4 further comprising a controller which opens the valve when said chamber pressure value corresponding to the pressure in the chamber is above said first pressure value.

6. A flywheel system according to claim 2 further comprising a pressure sensor for determining said chamber pressure value.

7. A flywheel system according to claim 1 wherein the valve includes a seal which selectively seals the passage and wherein the seal includes a face seal.

8. A flywheel system according to claim 1 further comprising a controller which maintains the valve in a closed state until the flywheel is rotating, and opens the valve after the flywheel begins rotating.

9. A flywheel system according to claim 1 further comprising a controller which starts the flywheel system by opening the valve following start-up of the flywheel system, when the vacuum pump is rotating at a speed in excess of a speed threshold value.

10. A flywheel system according to claim 1 further comprising a controller determines when rotation of the flywheel is to be shut down, and closes the valve before controlling said flywheel to come to rest.

11. A flywheel system according to claim 1 further comprising a controller which monitors a pump speed of said flywheel system, wherein the controller opens the valve when the pump speed is above a threshold value.

12. A flywheel system comprising: a flywheel; a chamber within which said flywheel is provided; a passage for connecting the chamber to an inlet of a vacuum pump; a valve arranged to selectively open or close said passage; and a controller which determines a chamber pressure value corresponding to a pressure in the chamber; determines a maximum allowable flywheel speed value based on the determined chamber pressure value; and controls the flywheel to limit the speed of the flywheel to be below the determined maximum allowable flywheel speed value.

13. A flywheel system according to claim 12 , wherein the controller decreases the determined maximum allowable flywheel speed value with increasing pressure in the chamber.

14. A method of controlling a flywheel system according to claim 12 , wherein the determined maximum allowable flywheel speed value is less than 10,000 rpm when the chamber pressure value is above 10 mbar.

15. A flywheel system comprising: a flywheel; a chamber within which said flywheel is provided; a passage for connecting the chamber to an inlet of a vacuum pump; and a valve which selectively opens or closes said passage, at least partially based upon a chamber pressure value corresponding to a pressure in the chamber, and wherein the valve opens the passage when said chamber pressure value exceeds a value that is between 4 and 8 mbar.

16. A flywheel system according to claim 15 further comprising a pressure sensor for determining said chamber pressure value.

17. A flywheel system according to claim 15 wherein the valve includes a seal for sealing the passage and wherein the seal includes a face seal.

18. A flywheel system according to claim 15 further comprising a controller which starts the flywheel system by maintaining the valve in a closed state until the vacuum pump is rotating; and opens the valve after the vacuum pump begins rotating.

19. A flywheel system according to claim 18 wherein the controller opens the valve when the vacuum pump is rotating at a speed in excess of a speed threshold value.

20. A flywheel system according to claim 15 further comprising a controller which determines when the flywheel system is to be shut down, and closes the valve before controlling the vacuum pump to come to rest.